The extended McEvily model for fatigue crack growth analysis of metal structures

An extended McEvily model for fatigue crack growth analysis of metal structures is proposed in this paper. In comparing with our previous work, the extension is mainly concerned with the following two aspects: (1) the slope of the fatigue crack growth rate curve is regarded as a variable rather than a fixed value for different materials; (2) both the maximum stress intensity factor at the crack opening level, Kop,max and the effective stress intensity factor range at the threshold level, ΔKeff,th are functions of load ratio, R and they are determined by the curve fitting method. Results indicate that the value of Kop,max tends to decrease slightly as load ratio increases where crack closure is experimentally detected. According to the present data obtained through the nonlinear least squares fitting method and discussions on the experimental results in the published literature, the parameter ΔKeff,th increases with increasing load ratios where crack closure exists and decreases at high load ratios where the experimental data are closure free. In this paper, all the parameters in the extended McEvily model are assumed to be unknown in advance and they are estimated through the curve fitting method based on the experimental data. The method is also put forward to determine material constants in the crack growth rate law based on the fitting parameters under different load ratios. Comparison between the predicted results and the corresponding experimental data with different load ratios reveals that the extended McEvily model can account for the load ratio effect reasonably well. Based on our previous work this model can also be expected to explain other fatigue phenomena.